<!DOCTYPE html>
<html lang="zh">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>DOM 1</title>
    <style>
        .red{
            background: red;
        }
    </style>
</head>

<body>
    示例
    <div id="test">grand
        <div id="son">son</div>
        <div class="son2">son2</div>
        <div class="son3">son3</div>
    </div>
    <div id="test2">grand
        <div class="son">son2</div>
    </div>
    <script src="dom.js"></script>
    <script src="main.js"></script>
</body>

</html>